A display device including a display portion that displays frame images successively switches the frame images displayed on the display portion on the basis of, for example, an input image signal from the outside to display smooth images on the display portion. A frequency for switching the frame images is called frame rate, and 60 Hz is used in general. It has been known a display device that detects whether an input image signal is a signal representing a still image or a signal representing a moving image and switches a frame rate according to a detection result (see, for example, Patent Literature 1).
When the input image signal represents the still image, the device described in Patent Literature 1 reduces the frame rate to reduce power consumption during display. When the input image signal is switched between the still image and the moving image and the frame rate is increased or reduced, a predetermined time constant is given to the frame rate to prevent the frame rate from suddenly changing. Consequently, deterioration in display quality of an image is prevented.
Patent Literature 1 discloses that the device further performs on-screen display for superimposing and displaying a menu image or the like on an input image displayed on the display portion on the basis of the input image signal. However, when the frame rate is reduced, if a moving image is on-screen displayed and the frame rate is gradually increased, the on-screen display image does not smoothly move and moves at intervals and display quality of the on-screen display image is deteriorated.